Chlamydia trachomatis is an obligate intracellular pathogen that is a leading cause of sexually transmitted disease. C. trachomatis infections have a high prevalence of morbidity and are also associated with pelvic inflammatory disease that often result in infertility. Despite considerable effort in the understanding of the pathogenesis of the disease, an efficacious chlamydial vaccine has not been attained. Chlamydia has evolved various strategies for evading defense mechanisms that have contributed to frequently asymptomatic and persistent infections in the host. It has been recently shown that C. trachomatis uses proteasome-like activity factor (CPAF) secreted intracellularly to evade adaptive immunity by inhibiting transcription factors required for major histocompatibility complex (MHC) expression. Therefore, neutralization of CPAF activity would normalize MHC expression and unmask the infected cells to immune surveillance and clearance. We have provided evidence to demonstrate the use of soluble interleukin (IL)-12 as a potent vaccine adjuvant for mucosal vaccination. IL-12 delivered non-invasively intranasally (i.n.) with recombinant CPAF greatly enhances protection against subsequent C. trachomatis infection. Secretory IgA is the principal immunoglobulin at mucosal surfaces. Importantly, IgA, unlike IgG, is translocated across epithelial tissue and been shown to neutralize pathogens intracellularly. Since C. trachomatis is an intracellular pathogen and produces CPAF to evade host defenses, vaccination strategies to enhance CPAF specific-secretory IgA production will be beneficial to the host. This proposal is designed to test several important aspects of the hypothesis by using animals with a targeted disruption in IgA gene expression (IgA-/- mice), and polymeric Ig receptor (plgR-/- mice), that have defective IgA transport into mucosal secretions. Specifically, we will optimize an intranasal vaccination approach using CPAF. Based on these studies, we will characterize cellular and humoral immune responses and determine the role of IgA in CPAF-induced immunity using IgA-/- mice. Finally, we will directly investigate the functional role of IgA in intracellular neutralization of CPAF activity during C. trachomatis infection.